Electrooptical system



LWESS Aug. 26, i930,

H. NYQUIST ELECTROPTICAL SYSTEM Filed July l5, 1928 A Ffa.

24 Gsmu A Tamm/Ey Patented Aug. 25, 1930 HARRY NYQUIST, OF MILLBURN, NEW JERSEY, ASSIGNOR TO AMERICAN TLEPHONE AND TELEGRABH COMPANY, A.A CORPORATION OF NEW YORK vnintrrnoorcLIcAI. SYSTEM Application .This invention relates to electro-optical systems, and rmore particularly to television. An object of the inventionis to reduce 1n- `terference effects, 'or ghost effects, in an 5 electro-optical image producing system caused by'currentsset up by an interfering image wave of another system orchannel. A further object is to provide simple means for rendering television transmission secret.

ence in television systems heretofore devised. In general, such systems'einploy current selective means so that the interfering energy is l prevented image whatsoever. In another arrangement heretofore known the image currents are produced intercurrently or alternately-for elemental periods and accordingly no interte'rf ence images are produced. l It is well'lmown that a faint. irregularity in the flat portion of apicture ,is considerably enhanced in visibility by being in the formof a definite pattern. In the same way faint intei-ference is enhanced in visibility if it is in the form of an intelligible image such refrom one television sults from interference In accordtransmlssion channel in another.

ance with this invention the eifect in thev image field resulting from interference 1s r 3'0 caused to bear little or no vresemblance to the interfering image and to be unintelligible. In generahthis is accomplished by arranging the scanning differently inthe two chan- `nels or systems.

In a lparticular arrangement illustrative of the invention scanning discs having the scanining apertures differentlyarrang'ed for the two channels are employed, each` channel -being substantially like that disclosed in a co-A pending application of H. E. Ives and Frank Gray, Serial No. 181/3581, filed April 6. 1927. The apertures for the discs of onechannel are arranged in a single turn while those in the disc for the other channel are arranged so that the adjoining elemental lines are not scanned successively but sivelyy scannedlines are separated as much as v possible. The discs at the transmitter and re. ceiver of any 'one channel are substantially identical.

Steps have been taken to prevent interferfrom producing any interfering' preferably succes- :liled July- 13, 1928. i Serial N. 292,540.A

',IVhile the invention is particularly useful for television, it isapplicable to other types of electro-optical systems, for example, photo-telegraphic systems. v

Amore detailed description of the inven. 55 tion follows and is villustrated in the accom.- panyingv drawings. A

v.Figure 1 is 'a schematic representation'of a plurality of transmitting and receiving television stations which maybe simultaneously operated and between which interference may occur. It may,'for example, be a single twoway system.

` Fig. 2 is ai drawing of a scanningdisc having apertures arranged to successively scan adjacent line series ofelemental areas .and adapted for use in one of Atwo interfering channels in vaccordance with this invention.

Fig` 3 is a drawing of Vanother form of a scanning disc whichmay be used in one of two interfering channels in carrying out this invention. It has apertures arranged to suc.

cessively scan non-adjacentline series of elemental areas. f

Fig. 4- is a drawing of a simple form of received image transmitted over one of two interfering channels of a system such as that shown in Fig. 1 when no cross pick-up interference occurs between channels.

` Fig. is a drawing of another simple form ofreceived image such asV ymight be transmitted over one of two interfering-channels of systems exempliied in'Fig. 1 when no cross pick-up. .interference occurs between channels.

F1g.1 6 is a drawing of the received image shown in Fig. 4 with a cross'pick-up imagesuperimposed thereupon resulting from interference from the channel over which the image of Fig. 5 is transmitted when ordinary terminal apparatus is employed. i

Fig. 7 is a drawing of the image field under the same. conditions-as that of Fig.. 6 but with'the use of terminal apparatus-.in accordance with kthis invention.

The schematic representation of Fig. 1 of a two-way television system illustrates in a K very simple way conditions under 'which crosstalk or cross pickup interference may 1 occur in a television system between a. plural- .100

ity of channels of a single system or between a plurality of separate interfering systems. T1 represents a transmitting station connected by channel L1 with a receiving station itl; and R2 represents a transmitting station connected by channel L2 with a receiving station R2, the transmission channels being in such proximity thatcross talk or cross pickup-interference may occur. fhile the two systems are shown as transmittingin opposite directions interference might equally well occur if both were simultaneously transmitting in the same direction. elaborate system or a larger network of svs-v tems a larger number of channels would simultaneously be in operation and a larger amount of interference might occur. This invention makes unintelligible any interference effect occurring under any of these conditions.

` The image areas shown in Figs. 4, 5, 6 and 7 are cross ruled into elemental areas in order to facilitate an understanding of their description. Fig. 4, and' likewise Fig. 5, represents both the picture or object whose image is transmitted and also the receivedimage when no crosstalk or cross pick-up interference occurs. Figs. 6 and 7 show a received image similar to that of Fig. l and the effects of cross pick-up from the image of Fig. 5. In Fig. 6 the cross pick-up image of Fig. 5, while not as distinct as the main image of Fig. 4 directly transmitted, issi'milar in form to the original and consequently intelligible. The received imagenin Fig. 7 for the main image is the Asame as in Fig. 6 but the cross pick-up image of Fig. 5 has been rendered unintelligible by a-repositioning of its ele* mental areas which results in lessening its disurbing effect. The received main and cross pick-up images as shown in Fig. 6 occur when :he scanning arrangement is identical in operation'for the interfering channels; while ;hereceived image and the cross pick-up eftect as shown in Fig. 7 result when the scanling disc aperture arrangements are dierant for each of the interfering channels simul- ;aneously in operation.

The scanning disc shown in Fig. 2 has a l)lurality of apertures arranged to successive y scan adjacent line series of elemental areas' ind the apertures in thiscase are arranged n a. uniform spiral. -This uniform spiral Lrrangement of the apertures is only one of a lumber of arrangements lwhich may be used. Phe scanningdisc shown in Fig. 3 has a plu- Iality of apertures arranged to successively can nonadjace'nt line series of elemental reas. An essential. requirement in this type f apparatus is that the arrangement of the 'elative positions ofthe apertures of the canning discs of two or more systems be uch that successively scanned lines are in ,ifferent positions and are preferably widely eparated for the di'erent systems between ln a more rrr/agree which interference may occur. The specilic arrangement of the apertures as here shown for the two scanning discs with relation to each other in part is as follows: Consider ing the angular position of the apertures in the order'as numbered on the scanning disc in Fig. 2, aperture in position No. 1 in Fig. 3 has a radial distance from the center of the disc the same as that of aperture No. 4 in Fig. 2, aperture in position No. 2 in Fig. 3 the same as that of No. ll in Fig. 2, aperture in position No. 3 in Fig. 3 the same as that of No. 18 in Fig. 2, aperture in position No. t of Fig. 3 the same as that of No. l of Fig. 2, etc., as indicated by these two figures. A complete comparison between the angular positions of the apertures and their radial positions as indicated on the scanning discs in Figs. 2 land 3 is given in Fig. 7. The numbers on the leftehand side of Fig. 7 in dicate the annular positions from the point of reference at the top of the scanning discs of Figs. 2 and 3. rlhe numbers at the righthand side of Fig. 7 indicate the interchange or scrambling of'the radial positiens for each angular position following the arrangement in- Fig. o. Other arrangements of the positioning of the apertures or the order of scanning to break up interference between images may obviously be made in any suitable manner. If either of the scanning discs shown ifi Figs. 2 and 3 is used at the terminal apparatus of each of the stations T1, R1, T2 and R2 of Fig. 1the receivedmain and cross pick-up images are as shown in Fig. 6, while if the scanning disc shown in Fig. 2 is used at the 'A terminal apparatus T1 and R1 and .the scan ning disc as shown in Fig. 3 is used by the terminal apparatus T2 and R2 the received main image and the cross pick-up effect are as shown in Fig. 7. In'Fig. 7 the faintly reproduced crosstall elemental areas of F ig. 5'

are equal in number to the elemental areas of Fig. 5, but are differently positioned. Two of them are superimposed `upon the lower line of elemental areas in the Amain image at line position 22 of the image field and are there-4 .fore not distinctively visible in the drmving.'l These superimposed cross pick-up elemental 'y .l U5,

areas occur at position 7 from the left and'7 from the right side of the image area.

imY

The numbers shown at theleft of Figs. 41,

5, 6 and 7 represent the scanning lines of the apertures l to 24 in the scanning disc of Fig. 2, while the numbers at the right of Fig. 7 represent the scanning lines as successively produced by the apertures in the scanning disc shown in Fig. 3.

It is obvious that the principle of making the received cros's pick-up interfering effect unintelligible as set forth herein may be car- '.ried out by various modifications ofthe scanning operation without departing from the principles of this invention. It should be noted too that in one aspect this invention ligible image.

.may be made permits the secret transmission of images, in that a station such as Rl, Fig. l, not equipped witha scanning disc such as those used at the terminals ofthe specially equipped system such as T2 R2 L2 can not pick up currents from the latter which will produce an intel- LikeWise a system such as T2 R2 L2 can not be successfully tapped with ordinary 'television apparatus. If it were desired to maintain secret transmission over T2 Rg L2 the arrangement of apertures could be kept secret and also changed at will by substituting different discs if desired.

In case the interfering systems orchannels are part of the same general system and it becomes desirable to enable each terminal station or radio station to communicate with each other such station, a plurality of discs available at each station so that a choice of discs may be made 'such that communication with any desired station and reduction of cross-interference effects in interfering channels lmay both be effected. such case all receiving sets and all transmitting sets' may be similar in every respect cxcept the scanning discs.

What is claimed is:

l ,An electro-optical image producingl sys' -tem comprising means for causing image currents produced in said system by an' interfering image Wave to set up in the image field of sai system an efectwhich bears' little or no resemblance-to the interfering image and is unintelligible, said means comprising moving scanning members for'respectively setting up and utilizing desired incoming image waves, said interfering Wave 'being set up by a system similar toijhat in which interference is set up eXceptfor the arrangement of the apertures of the scanning members.

2. In an electro-optical image producing A comprising a pluralityoff channels,

system for scanning successlvely' the elemental me GIDS areas of an image field 'in'oneorder for one of said channels of said system and. means for scanning successively the corresponding elemental areas of another similarly shaped image field in' a different order for another of said channels of said system, the orders being such that the image currents for transmission over one channel can produce only unintelligible images in the receiving termilnalfapparatus of the other channel.

3. In an electro-optical image producing system, equipment for two-way television over separate transmission channels, means for scanning successively the elemental areas -Y of the image field in one order for one direction of transmission. and in a different order for the opposite direction of transmission, the orders being such that the image currents for transmission in one direction can produce only unintelligible images in the equipment for transm1ssion 1n the other direction.

4. In an electro-optical image producing system, two channels located in such proximity to one another channel produce interfering currents in the other channel, scanning discs for one channel having scanning apertures arranged in a single spiral for scanning adjacent lines successively, and scanning discs for the other channel synchronized with those of the first channel and having apertures arranged so that successively scanned elemental areas are Widely separated, whereby interfering currents in either of the channels can produce only unintelligible images.

5. An electro-optical system arranged for simultaneously producing electrically a plurality of different images respectively of different fields of view of the same shape, and means for rendering unintelligible an interference effect Which may be superimposed upon one of'said images by interference energy set up by the image currents used in the production of any other image.

6. An electro-optical system having a plurality ,of channels and arranged for simultaneously transmitting and producing electrically a plurality spectively of different fields of view of the same'shape, and scanning means comprising moving apertured members and arranged to diversify the. order of the scanning of the elemental areas of said fields of viewso that` the scanning order is substantially different in any channel from that of any other channel. f

In testimony whereof, I have signed my name to this specification this July, 1928. A

HARRY NYQUIST.

of different `images re that image currents 1n one ioil' 

